This project will investigate cellular events that lead to the development of left ventricular dysfunction in experimental animals and patients with diabetes mellitus. Diabetes mellitus is associated with a cardiomyopathy characterized in part by impaired diastolic relaxation. In previous animal studies, we have defined biochemical features of this myopathy that suggest that chronic protein kinase C activation and subsequent phosphorylation of the thin filament protein, troponin I, is central to the maladaptation and also that this process can be abrogated by treatment with an AT1 receptor antagonist. The present application will extend these observations. Two parallel lines of investigation are proposed: 1. Studies in diabetic rats and mice will be performed to establish the effects of transcriptional and post-translation modification of thin myofilament proteins on the relaxation properties and contraction kinetics of isolated fibers. These will include troponin I exchange experiments in skinned fibers to establish the functional of significance of TnI phosphorylation and also studies in transgenic mice expressing TnI protein with a mutated PKC site. 2. Studies will be performed on cardiocytes isolated from the myocardium of patients with diabetes in order to establish whether the same biochemical and mechanical abnormalities are present in human heart disease. It is hoped that this pronged approach will allow the extension of a fundamental experimental observation to clinical practice.